The storage capacities of data storage systems have grown enormously. For example, EMC Corporation""s Symmetrix(copyright) data storage system can offer storage measured in Terabytes. To offer this storage, a Symmetrix(copyright) system pools a collection of physical disks (also referred to as xe2x80x9cspindlesxe2x80x9d).
Each physical disk can respond to a limited number of I/O (Input/Output) operations (e.g., read and write requests) in a given time period. The number of I/O operations a physical disk can handle is often measured in IOPS (Input/Output operations per second). To respond to I/O requests quickly and conserve IOPS, many systems use a high-speed cache (pronounced xe2x80x9ccashxe2x80x9d). For example, a cache can store copies of data also stored on a physical disk. If the system can respond to a request using a copy of data stored in the cache instead of retrieving data from the physical disk, the system has both reduced response time and reduced the I/O burden of the physical disks.
A cache can also speed responses to write requests. For example, the Symmetrix(copyright) system can store write requests in a cache and defer storage of the information to a physical disk until later. Thus, a host requesting the write operation receives fast confirmation of the write operation from the storage system even though the write operation has not yet completed.
In general, in one aspect, the description includes a method of responding to storage access requests. The method includes defining at least one write area and at least one read-only area, receiving a write request specifying a first address that resides within the at least one read-only area, determining a second address in the write address area, and storing data associating the first address with the second address.
Embodiments may include one or more of the following features. The method may further include storing information included in the write request at the second address. Determining the second address may include determining the next sequential address of a write area. The method may further include receiving a read request specifying the first address, accessing the data associating the first address and the second address, and requesting information stored at the second address. The method may further include redefining the write area and read area to form at least one new write area and at least one new read area where at least a portion of the new read-only area occupies an area previously occupied by the write area. The method may further include defining a third area for storing a copy of at least one of the read-only areas, copying data stored in at least one of the read-only areas into the third area, and collecting free blocks of the third area.
In general, in another aspect, the description includes a computer program product, disposed on a computer readable medium, for responding to storage access requests. The computer program includes instructions for causing a processor to define at least one write area and at least one read-only area, receive a write request specifying a first address that resides within the at least one read-only area, determine a second address in the write address area, and store data associating the first address with the second address.
In general, in another aspect, the description includes a method of managing storage. The method includes defining a read-only storage area, a write storage area, and a first garbage storage area. The method also includes repeatedly redirecting write requests for an address within the read-only storage area to the write area, collecting free space in the garbage storage area, and defining a new read-only storage area, a new write storage area, and a new garbage storage area such that the new read-only area includes the previously defined write area and the new write area includes collected free space in the new garbage storage area.
Embodiments may include one or more of the following features. The method may further include copying data stored in the new read-only storage area to the new garbage storage area. The storage areas may be physical storage areas. The write requests may specify a physical address.
In general, in another aspect, the description includes a system for handling I/O (Input/Output) requests. The system includes a collection of storage disks and a block table associating addresses specified by the I/O requests with addresses of the storage disk. The block table also defines at least one read-only area of the storage disks, at least one write area of the storage disks, and at least one third area of the storage disks. The system also includes instructions for causing a processor to process a read request by accessing the block table to determine the storage disk address associated with the-address specified by the request. The system also includes-instructions for causing a processor to process a write request that specifies a storage disk address corresponding to the at least one read-only area of the storage disks by determining a next location in the at least one write area and storing information in the block table that associates the location in the at least one write area with the storage disk address specified by the write request.
Advantages will become apparent in view of the following description, including the figures and the claims.